Question

Identify the factors of x2 − 4x − 12?
(x + 4)(x − 3)

(x − 4)(x + 3)

(x − 2)(x + 6)

(x + 2)(x − 6)

Answer 1

To do this in your head:

What are the prime factors of -12?
-1*2*2*3

What two things added together could be -4, things that must be pieces of the prime factorization above
6 + -2 = -4

Does 6 * -2 = -12? Yes.
6 = 2*3
-2 = -1*2


So all good. And that's how I do it in my head at a glance.